Clinical significance of RKIP mRNA expression in non-small cell lung cancer

Identification of cuproptosis and immune-related gene prognostic signature in lung adenocarcinoma

Background

Cuproptosis is a novel form of programmed cell death that differs from other types such as pyroptosis, ferroptosis, and autophagy. It is a promising new target for cancer therapy. Additionally, immune-related genes play a crucial role in cancer progression and patient prognosis. Therefore, our study aimed to create a survival prediction model for lung adenocarcinoma patients based on cuproptosis and immune-related genes. This model can be utilized to enhance personalized treatment for patients.

Methods

RNA sequencing (RNA-seq) data of lung adenocarcinoma (LUAD) patients were collected from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases. The levels of immune cell infiltration in the GSE68465 cohort were determined using gene set variation analysis (GSVA), and immune-related genes (IRGs) were identified using weighted gene coexpression network analysis (WGCNA). Additionally, cuproptosis-related genes (CRGs) were identified using unsupervised clustering. Univariate COX regression analysis and least absolute shrinkage selection operator (LASSO) regression analysis were performed to develop a risk prognostic model for cuproptosis and immune-related genes (CIRGs), which was subsequently validated. Various algorithms were utilized to explore the relationship between risk scores and immune infiltration levels, and model genes were analyzed based on single-cell sequencing. Finally, the expression of signature genes was confirmed through quantitative real-time PCR (qRT-PCR), immunohistochemistry (IHC), and Western blotting (WB).

Results

We have identified 5 Oncogenic Driver Genes namely CD79B, PEBP1, PTK2B, STXBP1, and ZNF671, and developed proportional hazards regression models. The results of the study indicate significantly reduced survival rates in both the training and validation sets among the high-risk group. Additionally, the high-risk group displayed lower levels of immune cell infiltration and expression of immune checkpoint compared to the low-risk group.

Understanding Mechanisms of RKIP Regulation to Improve the Development of New Diagnostic Tools

Simple Summary

Raf Kinase Inhibitor protein is a protein that governs multiple intracellular signalling involved primarily in the progression of tumours and the development of metastases. In this review, we discussed the main mechanisms that regulate the expression and activity of RKIP with the aim of identifying the link between the transcriptional, post-transcriptional and post-translational events in different tumour settings. We also tried to analyse the studies that have measured the levels of RKIP in biological fluids in order to highlight the possible advantages and potential of RKIP assessment to obtain an accurate diagnosis and prognosis of various tumours.

Abstract

One of the most dangerous aspects of cancer cell biology is their ability to grow, spread and form metastases in the main vital organs. The identification of dysregulated markers that drive intracellular signalling involved in the malignant transformation of neoplastic cells and the understanding of the mechanisms that regulate these processes is undoubtedly a key objective for the development of new and more targeted therapies. RAF-kinase inhibitor protein (RKIP) is an endogenous tumour suppressor protein that affects tumour cell survival, proliferation, and metastasis. RKIP might serve as an early tumour biomarker since it exhibits significantly different expression levels in various cancer histologies and it is often lost during metastatic progression. In this review, we discuss the specific impact of transcriptional, post-transcriptional and post-translational regulation of expression and activation/inhibition of RKIP and focus on those tumours for which experimental data on all these factors are available. In this way, we could select how these processes cooperate with RKIP expression in (1) Lung cancer; (2) Colon cancer, (3) Breast cancer; (4) myeloid neoplasm and Multiple Myeloma, (5) Melanoma and (6) clear cell Renal Cell Carcinoma. Furthermore, since RKIP seems to be a key marker of the development of several tumours and it may be assessed easily in various biological fluids, here we discuss the potential role of RKIP dosing in more accessible biological matrices other than tissues. Moreover, this objective may intercept the still unmet need to identify new and more accurate markers for the early diagnosis and prognosis of many tumours.

Computational Analyses of YY1 and Its Target RKIP Reveal Their Diagnostic and Prognostic Roles in Lung Cancer

Simple Summary

Lung cancer (LC) is the tumor with the highest global mortality rate. Novel personalized therapies are currently being tested (e.g., targeted inhibitors, the immune-checkpoint inhibitors), but they cannot yet prevent the very frequent relapse and generalized metastases observed in a large population of LC patients. Currently, there is an urgent need for novel reliable biomarkers for the prognosis and diagnosis of LC. Through the systematic analysis of multiple deposited expression datasets, this report aims to explore the role of the Yin-Yang 1 (YY1) transcription factor and its target the Raf Kinase Inhibitory Protein (RKIP) in LC. The computational analysis suggested the predictive diagnostic and prognostic roles for both YY1 and RKIP stimulating further studies for proving their implication as novel biomarkers, as well as therapeutically druggable targets in LC.

Abstract

Lung cancer (LC) represents a global threat, being the tumor with the highest mortality rate. Despite the introduction of novel therapies (e.g., targeted inhibitors, immune-checkpoint inhibitors), relapses are still very frequent. Accordingly, there is an urgent need for reliable predictive biomarkers and therapeutically druggable targets. Yin-Yang 1 (YY1) is a transcription factor that may work either as an oncogene or a tumor suppressor, depending on the genotype and the phenotype of the tumor. The Raf Kinase Inhibitory Protein (RKIP), is a tumor suppressor and immune enhancer often found downregulated in the majority of the examined cancers. In the present report, the role of both YY1 and RKIP in LC is thoroughly explored through the analysis of several deposited RNA and protein expression datasets. The computational analyses revealed that YY1 negatively regulates RKIP expression in LC, as corroborated by the deposited YY1-ChIP-Seq experiments and validated by their robust negative correlation. Additionally, YY1 expression is significantly higher in LC samples compared to normal matching ones, whereas RKIP expression is lower in LC and high in normal matching tissues. These observed differences, unlike many current biomarkers, bear a diagnostic significance, as proven by the ROC analyses. Finally, the survival data support the notion that both YY1 and RKIP might represent strong prognostic biomarkers. Overall, the reported findings indicate that YY1 and RKIP expression levels may play a role in LC as potential biomarkers and therapeutic targets. However, further studies will be necessary to validate the in silico results.

Insights of RKIP-Derived Suppression of Prostate Cancer

Simple Summary

Despite an intensive research effort in the past few decades, prostate cancer (PC) remains a top cause of cancer death in men, particularly in the developed world. The major cause of fatality is the progression of local prostate cancer to metastasis disease. Treatment of patients with metastatic prostate cancer (mPC) is generally ineffective. Based on the discovery of mPC relying on androgen for growth, many patients with mPC show an initial response to the standard of care: androgen deprivation therapy (ADT). However, lethal castration resistant prostate cancers (CRPCs) commonly develop. It is widely accepted that intervention of metastatic progression of PC is a critical point of intervention to reduce PC death. Accumulative evidence reveals a role of RKIP in suppression of PC progression towards mPC. We will review current evidence and discuss the potential utilization of RKIP in preventing mPC progression.

Abstract

Prostate cancer (PC) is a major cause of cancer death in men. The disease has a great disparity in prognosis. Although low grade PCs with Gleason scores ≤ 6 are indolent, high-risk PCs are likely to relapse and metastasize. The standard of care for metastatic PC (mPC) remains androgen deprivation therapy (ADT). Resistance commonly occurs in the form of castration resistant PC (CRPC). Despite decades of research efforts, CRPC remains lethal. Understanding of mechanisms underpinning metastatic progression represents the overarching challenge in PC research. This progression is regulated by complex mechanisms, including those regulating PC cell proliferation, epithelial–mesenchymal transition (EMT), and androgen receptor (AR) signaling. Among this PC metastatic network lies an intriguing suppressor of PC metastasis: the Raf kinase inhibitory protein (RKIP). Clinically, the RKIP protein is downregulated in PC, and showed further reduction in mPC. In xenograft mouse models for PC, RKIP inhibits metastasis. In vitro, RKIP reduces PC cell invasion and sensitizes PC cells to therapeutic treatments. Mechanistically, RKIP suppresses Raf-MEK-ERK activation and EMT, and modulates extracellular matrix. In return, Snail, NFκB, and the polycomb protein EZH2 contribute to inhibition of RKIP expression. In this review, we will thoroughly analyze RKIP’s tumor suppression actions in PC.

Methods to Study Posttranslational Modification Patterns in Cytotoxic T-Cells and Cancer

Protein posttranslational modifications (PTMs) regulate intracellular signaling associated with development and progression of many diseases; thus, they are key to understanding pathological mechanisms and set up more tailored therapies. In addition, many posttranslationally modified proteins are released into biological fluids and can be used as new and more specific biomarkers. Based on this evidence, we analyzed the role of some PTMs in cancer and described the correlation between specific PTMs and T-cells activation/inhibition in cancer microenvironment. In the second part of this chapter, we analyzed the most commonly used approaches for qualitative and quantitative determination of PTMs. The comparison of three distinct but often complementary methodologies such as immunoblotting, mass spectrometry, and ELISA assays has allowed to highlight the pros and cons of each approach with a focus on their current application and their future developments to obtain more confident biomarkers and therapeutic targets useful for diagnosis, prognosis, and monitoring of the response to therapy.

Overexpression of Raf-1 kinase inhibitor protein inhibits cell invasion and migration in lung cancer cells through suppressing epithelial-mesenchymal transition

Background

Raf-1 kinase inhibitor protein (RKIP) is a small evolutionary conserved protein that was associated with the Raf-MEK-ERK pathway. However, whether RKIP would alter the invasion and metastasis of non-small cell lung cancer (NSCLC) and play the role through suppressing epithelial-mesenchymal transition (EMT) remains to be explored.

Methods

A549 cells were transfected with RKIP-GV141 plasmid for overexpression of RKIP. Colony formation assay and MTT assay were performed to measure the effects of RKIP on the proliferation and cell viability assay of A549 cells. Transwell, Migration Assay and wound healing assay were performed to analyze the effects of RKIP on the invasion and metastasis of A549 cells. E-cadherin and vimentin were measured by Western blot to conform RKIP affects invasion and metastasis of NSCLC via inhibiting EMT.

Results

RKIP is downregulated in NSCLC tissues compared to adjacent normal lung tissues by IHC. Decreased expression of RKIP contributes to poor prognosis in lung adenocarcinoma patients. Age and pTNM stage were independent prognostic factors for adenocarcinoma patients. Overexpression of RKIP reduces the cell viability and limits the proliferation, invasion, and migration of A549 cells in vitro. Wound healing assay showed the degressive ability of metastasis. High expression of E-cadherin and low expression of vimentin indicated that RKIP affects invasion and metastasis of NSCLC via inhibiting EMT.

Conclusions

RKIP is decreased in NSCLC tissues. Overexpression of RKIP in A549 cells would decrease the cellular proliferation, viability, invasion ability, and metastasis ability probably via inhibiting EMT through upregulating E-cadherin expression and downregulating vimentin expression.

Current Status of Raf Kinase Inhibitor Protein (RKIP) in Lung Cancer: Behind RTK Signaling

Lung cancer is the most deadly neoplasm with the highest incidence in both genders, with non-small cell lung cancer (NSCLC) being the most frequent subtype. Somatic mutations within the tyrosine kinase domain of the epidermal growth factor receptor (EGFR) gene are key drivers of NSCLC progression, with EGFR inhibitors being particularly beneficial for patients carrying the so-called “EGFR-sensitizing mutations”. However, patients eventually acquire resistance to these EGFR inhibitors, and a better knowledge of other driven and targetable proteins will allow the design of increasingly accurate drugs against patients’ specific molecular aberrations. Raf kinase inhibitory protein (RKIP) is an important modulator of relevant intracellular signaling pathways, including those controlled by EGFR, such as MAPK. It has been reported that it has metastasis suppressor activity and a prognostic role in several solid tumors, including lung cancer. In the present review, the potential use of RKIP in the clinic as a prognostic biomarker and predictor of therapy response in lung cancer is addressed.

Drosophila PEBP1 inhibits intestinal stem cell aging via suppression of ERK pathway

The intestine is a high cellular turnover tissue largely dependent on the regenerative function of stem cell throughout life, and a signaling center for the health and viability of organisms. Therefore, better understanding of the mechanisms underlying the regulation of intestinal stem cell (ISC) regenerative potential is essential for the possible intervention of aging process and age-related diseases. Drosophila midgut is a well-established model system for studying the mechanisms underlying ISC regenerative potential during aging. Here, we report the requirement of Drosophila phosphatidylethanolamine binding protein 1 (PEBP1) in ISC regenerative potential. We showed that PEBP1 was strongly expressed in enterocytes (ECs) of guts and its decrease with age and oxidative stress. Furthermore, the downregulation of PEBP1 in ECs accelerates ISC aging, as evidenced by ISC hyper-proliferation, γH2AX accumulation, and centrosome amplification, and intestinal hyperplasia. The decrease in PEBP1 expression was associated with increased extracellular signal-regulated kinase (ERK) activity in ECs. All these phenotypes by EC-specific depletion of PEBP1 were rescued by the concomitant inhibition of ERK signaling. Our findings evidence that the age-related downregulation of PEBP1 in ECs is a novel cause accelerating ISC aging and that PEBP1 is an EC-intrinsic suppressor of epidermal growth factor receptor (EGFR)/ERK signaling. Our study provides molecular insights into the tight regulation of EGFR/ERK signaling in niches for stem cell regenerative potential.

Clinical utility of microRNA-378 as early diagnostic biomarker of human cancers: a meta-analysis of diagnostic test

A meta-analysis was performed to evaluate the diagnostic value of miR-378 for detecting human cancers. Systematic electronic searches were conducted in PubMed, Web of Science, Embase, China National Knowledge Infrastructure, and Wanfang from the inception to January 15, 2016. We used the bivariate mixed effects models to estimate the combined sensitivity, specificity, PLRs (positive likelihood ratios), NLR (negative likelihood ratios), DORs (diagnostic odds ratios) and their 95% CI (confidence intervals) for assessing the diagnostic performance of miR-378 for cancers. Twelve studies were included in the meta-analysis, with a total number of 1172 cancer patients and 809 health controls. The overall estimated sensitivity and specificity were 0.75 and 0.74. The pooled PLR was 2.91, NLR was 0.34, DOR was 8.50, and AUC (Area Under the Curve) was 0.81. The subgroup analyses suggested that AUC for plasma-based is higher than serum-based. The overall diagnostic values of miR-378 in the present meta-analyses are moderate accurate for human cancers; The source of specimen has an effect on the diagnostic accuracy. The diagnostic value of serum-based was higher than that of plasma-based.

RKIP reduction enhances radioresistance by activating the Shh signaling pathway in non-small-cell lung cancer

Non-small-cell lung cancer (NSCLC) is exceptionally deadly because the tumors lack sensitive early-stage diagnostic biomarkers and are resistant to radiation and chemotherapy. Here, we investigated the role and mechanism of Raf kinase inhibitory protein (RKIP) in NSCLC radioresistance. The clinical data showed that the RKIP expression level was generally lower in radioresistant NSCLC tissues than in radiosensitive tissues. Reduced RKIP expression was related to NSCLC radioresistance and poor prognosis. In vitro experiments showed that RKIP knockdown increased radioresistance and metastatic ability in NSCLC cell lines. Mechanistically, RKIP reduction activated the Shh signaling pathway by derepressing Smoothened (Smo) and initiating glioma-associated oncogene-1 (Gli1)-mediated transcription in NSCLC. In addition, the inappropriately activated Shh–Gli1 signaling pathway then enhanced cancer stem cell (CSC) expression in the cell lines. The increasing quantity of CSCs in the tumor ultimately promotes the radiation resistance of NSCLC. Together, these results suggest that RKIP plays a vital role in radiation response and metastasis in NSCLC. RKIP reduction enhances radioresistance by activating the Shh signaling pathway and initiating functional CSCs. This role makes it a promising therapeutic target for improving the efficacy of NSCLC radiation treatment.

Overexpression of RKIP and its cross-talk with several regulatory gene products in multiple myeloma

Multiple myeloma (MM) is a clonal plasma-cell neoplastic disorder arising from an indolent premalignant disease known as monoclonal gammopathy of undetermined significance (MGUS). MM is a biologically complex heterogeneous disease reflected by its variable clinical responses of patients receiving the same treatment. Therefore, a molecular identification of stage-specific biomarkers will support a more individualized precise diagnostic/prognostic approach, an effective therapeutic regime, and will assist in the identification of novel therapeutic molecular targets. The metastatic suppressor/anti-resistance factor Raf-1 kinase inhibitor protein (RKIP) is poorly expressed in the majority of cancers and is often almost absent in metastatic tumors. RKIP inhibits the Raf/MEK/ERK1/2 and the NF-κB pathways. Whereby all tumors examined exhibited low levels of RKIP, in contrast, our recent findings demonstrated that RKIP is overexpressed primarily in its inactive phosphorylated form in MM cell lines and patient-derived tumor tissues. The underlying mechanism of RKIP overexpression in MM, in contrast to other tumors, is not known. We examined transcriptomic datasets on Oncomine platform (Life Technologies) for the co-expression of RKIP and other gene products in both pre-MM and MM. The transcription of several gene products was found to be either commonly overexpressed (i.e., RKIP, Bcl-2, and DR5) or underexpressed (i.e., Bcl-6 and TNFR2) in both pre-MM and MM. Noteworthy, a significant inverse correlation of differentially expressed pro-apoptotic genes was observed in pre-MM: overexpression of Fas and TNF-α and underexpression of YY1 versus expression of anti-apoptotic genes in MM: overexpression of YY1 and underexpression of Fas and TNF-α. Based on the analysis on mRNA levels and reported studies on protein levels of the above various genes, we have constructed various schemes that illustrate the possible cross-talks between RKIP (active/inactive) and the identified gene products that underlie the mechanism of RKIP overexpression in MM. Clearly, such cross-talks would need to be experimentally validated in both MM cell lines and patient-derived tumor tissues. If validated, the differential molecular signatures between pre-MM and MM might lead to a more precise diagnosis/prognosis of the disease and disease stages and will also identify novel molecular therapeutic targets for pre-MM and MM.

Reduced RKIP expression levels are associated with frequent non-small cell lung cancer metastasis and STAT3 phosphorylation and activation

The current study examined the role of Raf kinase inhibitor protein (RKIP) in non-small cell lung cancer (NSCLC) metastasis. A total of 100 patients with NSCLC were recruited following pathological diagnosis in the First Affiliated Hospital of Bengbu Medical College. The patients were classified and statistically analyzed according to their clinicopathological characteristics and tumor-node-metastasis stage. Paired tumor tissue and adjacent non-tumor tissue samples were subject to pathological diagnosis and western blot analysis. Transient transfection and lentivirus particle vector-mediated RKIP overexpression, small interfering RNA-mediated silencing, Transwell assays and immunocytochemistry methods were employed to elucidate the role and underlying mechanisms of RKIP and the Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway in NSCLC metastasis. Furthermore, in order to examine the in vivo effects of RKIP, recombinant lentivirus particles containing the RKIP gene were administrated in a mouse NSCLC tumor model via tail vein injection. The results revealed reduced RKIP expression levels in NSCLC tissue compared with corresponding non-cancer tissue. Additionally, RKIP expression levels were inversely associated with NSCLC intra-lung, lymph node and long-distance metastasis. The results also indicated that RKIP was able to block STAT3 activation via phosphorylation and inhibit NSCLC-cell metastasis in vitro. Furthermore, RKIP knockdown was able to promote STAT3 phosphorylation and cell metastasis in NSCLC cell lines. During in vivo experiments, RKIP overexpression was able to suppress xenograft tumor metastasis in nude mice. Therefore, RKIP may be an important factor in cancer cell metastasis in patients with NSCLC, and RKIP may inhibit NSCLC-cell invasion by blocking the activation of the JAK/STAT3 signaling pathway.

Insights into the application of let-7 family as promising biomarker in cancer screening

Cancer is a leading cause of death worldwide with its low 5-year survival rate. Studies on the accuracy of let-7 family for human cancers have inconsistent conclusions, leading us to conduct this meta-analysis. This meta-analysis comprised of 11 studies from eight articles involving 805 cancer patients and 483 controls. The pooled parameters were as follows: sensitivity, 77 % (95 % confidence interval (CI) 73-81 %); specificity, 80 % (95 % CI 68-88 %); positive likelihood ratio (PLR), 3.8; negative likelihood ratio (NLR), 0.29; and diagnostic odds ratio (DOR) 13.0. In addition, we plotted the SROC and calculated the area under the curve (AUC) of 0.81 (95 % CI 0.78-0.84), which indicated a relatively high descriptive accuracy. In summary, our data suggested that let-7 family might be applied in noninvasive screening tests for human cancers, which needed to be validated in further large-scale studies.

The clinical utility of microRNA-21 as novel biomarker for diagnosing human cancers

With cancer being a major cause of death worldwide, microRNAs (miRNAs) have been investigated as novel and non-invasive biomarkers for cancer diagnosis. Recently, microRNA-21 (miR-21) attracts much attention for its aberrant expression and has been widely studied in various cancers. However, the inconsistent results from studies make it hard to evaluate the diagnostic value of miR-21 in cancer diagnosis, which lead us to conduct this meta-analysis. We conducted a comprehensive literature search in the Medline, Embase, PubMed, CNKI, and Web of Science before July 1, 2014. STATA 12.0 software was used for calculation and statistical analysis. The pooled sensitivity, specificity, positive and negative likelihood ratio (PLR, NLR), and diagnostic odds ratio (DOR) were used to assess the diagnostic performance of miR-21 for cancers. Seventy-three studies in 60 articles were involved in this meta-analysis, with a total of 4684 patients with cancer and 3108 controls. The overall parameters were calculated from all the included studies: sensitivity of 0.78 (95% confidence interval (CI) 0.74-0.81), specificity of 0.83 (95% CI 0.80-0.86), PLR of 4.5 (95% CI 3.8-5.4), NLR of 0.27 (95% CI 0.23-0.32); DOR of 17 (95% CI 12-23), and area under the curve (AUC) of 0.88 (95% CI 0.84-0.90). In addition, we performed subgroup analyses based on ethnicity, cancer types, and sample types. Results from subgroup analysis showed that cancer types and sample types were the sources of heterogeneity in our meta-analysis. The overall diagnostic value of miR-21 is not very high for cancer diagnosis; however, it is affected significantly by the types of cancer and specimen. MiR-21 has a relatively high diagnostic value for detecting breast cancer, and miR-21 assays based on plasma, serum, and tissue achieved relatively higher accuracy.

MicroRNAs used as novel biomarkers for detecting cancer metastasis

The low survival rates of cancers are primarily due to late diagnosis and metastasis. Discriminating the metastasis is a crucial factor for prognosis and improving the survival rate of cancer patients. MicroRNAs (miRNAs) can regulate the expression of hundreds of downstream genes, which has a broad effect on the regulation of the whole cell cycle. Accumulating studies have found that the aberrant expression of miRNAs is associated with cancer genesis. The aim of this study is to evaluate the diagnostic value of miRNAs in detecting cancer metastasis. Medline, PubMed, Embase, and CNKI were searched for relevant articles. Sensitivity, specificity, positive and negative likelihood ratio (PLR, NLR) and diagnostic odds ratio (DOR), the summary receiver operator characteristic (SROC) curve and the calculated AUC (area under the SROC curve) were applied to explore the diagnostic accuracy of miRNAs in metastasis. Seven hundred seventy-one metastatic cancer patients and 552 non-metastatic cancer controls from 14 articles were involved in our meta-analysis. A sensitivity of 0.75 (95% confidence interval (CI), 0.72-0.79) and a specificity of 0.80 (95% CI, 0.76-0.84) were observed from metastatic patients and non-metastatic controls in the combined analysis. And the AUC was 0.83 (95% CI, 0.79-0.86). In addition, results from subgroup analyses suggested that a higher diagnostic value for metastasis was acquired in tissue sample other than blood sample (sensitivity, 0.82 versus 0.73; specificity, 0.84 versus 0.79; PLR, 5.0 versus 3.5; NLR, 0.22 versus 0.34; DOR, 23 versus 10; AUC, 0.88 versus 0.80). In summary, this meta-analysis proved the relatively high diagnostic value of miRNA in metastasis, which might be applied as a novel screening tool to detect metastasis along with other biomarkers. We also illustrated that tissue-based miRNAs may have a better diagnostic accuracy than blood-based miRNAs.

Diagnostic value of microRNA-21 in the diagnosis of lung cancer: evidence from a meta-analysis involving 11 studies

Molecular biomarkers that can be detected in easily accessible body fluids have been proposed as non-invasive, cost-effective, and useful tools for cancer diagnosis. Recently, extensive research has explored the involvement of the aberrant expression of microRNA-21 (miRNA-21, miR-21) in lung cancer. Inconsistent results, however, have prevented its widespread use in diagnosis. In light of this situation, our meta-analysis aimed to systematically determine whether aberrant miR-21 expression can distinguish patients with lung cancer from cancer-free controls with a high level of diagnostic accuracy. A comprehensive literature search for relevant studies published before December 23, 2013 was conducted in the MEDLINE, EMBASE, the Cochrane Library, and three Chinese databases. The pooled sensitivity, specificity and other parameters were used to assess the overall performance of miR-21-based assays. Statistical analysis was conducted using the STATA 11.0 software. Eleven research articles involving 676 patients with lung cancer and 529 healthy controls were considered eligible for inclusion in the present meta-analysis. The following summary parameters were calculated from all the included studies: sensitivity of 0.66 (95 % confidence interval [CI]: 0.57-0.74), specificity of 0.82 (95 % CI: 0.74-0.88), positive likelihood ratio (PLR) of 3.70 (95 % CI: 2.50-5.60), negative likelihood ratio (NLR) of 0.42 (95 % CI: 0.32-0.54); diagnostic odds ratio (DOR) of 9.00 (95 % CI: 5.00-16.00), and area under the curve (AUC) of 0.81 (95 % CI: 0.77-0.84). In addition, we added two pre-specified covariates (ethnicity and specimen types) to the bivariate model to assess their impact on the diagnostic value of miR-21 for lung cancer. Similar results were also observed in subgroup analyses, indicating a relatively low level of accuracy. The current meta-analysis indicates that a single miR-21 may not be sufficient to identify lung cancer and that more miRNAs should be used to detect lung carcinoma.